Well production method using radioactive



March 3, 1964 5. J. LIMANEK 3,123,708

WELL PRODUCTION METHOD USING RADIOACTIVE TRACERS TO ESTABLISH TWO NULL POSITION Filed Dec. 31, 1959 face/def 22 24 32/ United States Patent 3,123,708 WELL PRODUCTION METHOD USING RADIO- ACTIVE TRACERS TO ESTABLISH TWO NULL POSITION Stephen J. Limanek, Pleasantvilie, N.Y., assignor to Texaco Development Corporation, New York, N.Y., a corporation of Delaware Filed Dec. 31, 1959, Ser. No. 863,249 5 Claims. (Cl. 250-435) This invention relates to fluid production in a well or borehole and, more particularly, to a method of determin ing the amount and the nature of the fluid that enters a borehole from any given vertical interval of a well.

In accordance with this invention, a method is provided wherein fluids entering into a borehole are divided into three streams so as to provide a fluid interface or null point between adjacent fluids in the borehole. In the practice of this invention a first string of tubing is lowered into a borehole to a point within a zone of interest and a second string of tubing is lowered into the borehole to a point below the zone of interest. The borehole fluid is discharged from the borehole in three streams, a first stream being formed by the fluid flow through the first string of tubing, a second stream being formed by the fluid flow through the second string of tubing and a third stream being formed by the fluid flow in the annular space between the wall of the borehole, or a borehole casing, and the tubings. If the well has sufficient pressure, the fluid flow in the three streams may be controlled by employing a suitable valve in each stream, but if the well is a pumping well, the fluid flow in the three streams may be controlled by employing a suitable pump in each stream, or by a combination of one or more pumps and valves. By regulating the flow of the fluid the two fluid interfaces or null points formed by the three streams in the annulus may be positioned at any two depths in a zone of interest in the well. The interfaces may be readily located in the borehole by introducing in the annulus into one of two streams forming an interface a radioactive substance and measuring radioactivity at a point spaced from the point at which the radioactive substance is introduced into the stream to determine the direction of flow of the fluid and repeating the above steps at a plurality of points in the zone of interest in the borehole until a change in the direction of fluid flow is noted. If desired the locations of the fluid interfaces or null points may be determined by employing one or more well-known fluid de tectors which are electrically or mechanically sensitive to fluid movement. The fluid movement detectors may be in the form of torsion wires, impellers or fluid activated bridges having electrical outputs which may be transmitted to the earths surface. After the two interfaces are located, the amount and nature of the fluid in each of the three streams may be readily determined at the earths surface.

In one important aspect of this invention a productivity profile log of a zone of interest may be made by moving two interfaces formed by three streams through the zone of interest while varying the fluid flow rates in at least two streams and noting the locations of the interfaces and the amount and nature of the fluids flowing in each of the streams.

In order to more clearly understand this invention reference may be had to the accompanying drawing in which the figure is a vertical sectional view of a well or borehole traversing a producing formation showing the arrangement of the apparatus employed in accordance with this invention.

Referring to the drawing in more detail, a well or borehole is illustrated as passing through a producing formation 12. The upper portion of the well 10 is pro- ICC vided with a conventional casing 14 closed at the top by means of a suitable casing head 16. Passing down through the borehole 10 to a point within the vertical limits of the formation 12, and preferably to a point near one of these limits, is a first string of tubing 18. Also extending down through the borehole 10 to a point below the producing formation 12 is a second string of tubing 29. A first control valve 22 and a suitable flow meter 24 are provided at the upper end of the first string of tubing 18 which serve to control and measure the flow rate of a first stream of fluid 26. A second control valve 23 and a second flow meter 30 are provided in the upper end of the second string of tubing 28 which serve to control and measure the rate of flow of a second stream of fluid 32. A first interface or null point 34 will exist between the two bodies or streams of fluid 26 and 32. A third control valve 36 and a third flow meter 38 are coupled to the casing head 16 so as to control and measure the rate of fluid flow of a third stream 40 which passes upwardly in the borehole in the annular space between the casing 14 or the walls of the borehole 1i) and the tubings 18 and 20. A second interface or null point 42 will exist between the first and third bodies or streams of fluids 26 and 40. By properly adjusting the flow rates of the three fluid streams the two interfaces 34 and 42 can be moved along the wall of the borehole and at any desired spacing from each other.

Shown as suspended within the annulus in the borehole 10 on a conductor cable 44 is a first radiation detector 46 suitable for detecting the presence of radioactive substance in the borehole fluid. Beneath detector 46 is a source of radioactive substance 48, for example a gamma emitting substance. The latter (source 48) is supported by the first radiation detector 46; and a second radiation detector 50, which may be similar to the first radiation detector 46, is supported by the radioactive source 48 and electrically connected to the lower end of cable 44. The cable 44 passes upwardly over a suitable cable measuring device 52 which indicates or measures continuously the depth of the radiation detectors 46 and 5t and radioactive source 48 in the borehole 10. The cable 44 is connected at its upper end to a conventional recorder 54 capable of recording the output voltages from the first and second radiation detectors 46 and 50.

In one form of the method of this invention the amount of fluid flowing from a zone of interest into the borehole is determined by dividing the fluid flowing into the borehole into three streams. The rate of flow of the first stream 26 which passes through the first string of tubing 18 is set at a predetermined percentage of the total fluid flowing out of the borehole and maintained constant at all times. The rate of flow of the other two strearns, that is, the stream 32 flowing through the second string of tubing 20 and the stream 40 flowing up the annulus through valve 36 is varied by increments equal to the predetermined percentage while maintaining the total fluid flow constant.

More specifically, the total flow rate of the three streams is kept constant while the flow rate of the first stream 26 is adjusted to a predetermined value such as 10% of the total flow rate. The amount of fluid flowing from a first vertical interval of a zone of interest, such as producing formation 12, may be determined by establishing flow rates of 10%, and 0% of the total flow rate for the first, second and third streams, respectively, while the lower end of the first tubing 18 is held near the upper limit of the formation 12 within the first vertical interval. Assuming that there is no fluid flow into the borehgole above the formation 12, the second interface 42, which is the interface between the first and third bodies of fluid 26 and 40, will become established at the upper limit of the formation 12, as shown in the figure of the drawing. The other interface 34 will become stabilized at a point in the borehole 10 somewhat below the interface '42 depending upon the amount of fluid flowing to the borehole from the upperportion of the producing formation 12. The location of these two interfaces 34 and 42 can be readily detected by passing the radiation source 43, which is adapted to emit a radioactive substance into the borehole fluid, through the borehole and by means of the radiation detectors 46 and '50 spaced apart above and below, respectively, the radiation source 48 determining the direction of the fluid flow by detecting the radioactivity in the borehole fluid at each of the detector locations. After the two interfaces are located it is known that the rate of fluid flow into the borehole from the formation 12 in the interval between the location of the two interfaces 34 and 42 is equal to the rate of flow of the first stream, that is, to 10% of the total rate of flow of the three streams.

The tubing 13 is then lowered to a position just below the location of the first stabilized lower interface 34, the rates of flow of the streams are adjusted so that the rates of flow of the first, second and third fluid streams are equal to 10, 80 and 10 percent, respectively. After the two interfaces 34 and 42 again become stabilized, the radiation source 48 and the two detectors 46 and 50 are passed throught the zone of interest in the borehole to again locate the position of the two interfaces 34 and 42.

It can be seen that the upper interface 42 will now stabilize at the location of the first stabilized lower interface 34. Since the predetermined rate of flow of the first stream, that is, 10% of the total flow, is again flowing into the borehole from the second interval of the formation 12 defined by the two interfaces 34- and 42 which are again stabilized, it will be known that 10% of the total fluid flow is also flowing out of this second interval which lies immediately below the first interval. It can be seen that the length of the vertical interval between each of the stabilized interfaces 3'4 and 42 may differfor each ratio of flow rates of the second and third streams depending upon the amount of fluid flowing from the various portions of the producing formation 12. The rates of flow of the second and third streams are repeatedly varied until the rate of fluid flowing into the borehole from the lowermost portion of the producing formation 12 is determined, that is, until 90% of the total rate of flow of fluid is flowing in the third stream and is flowing in the second stream.

Although the above-described procedure calls for flow rate changes of increments equal to the rate of flow of the first fluid stream which will automatically position a succeeding upper interface or null point at the location of the preceding stabilized lower inter-face, the rates of change of the second and third streams may be different from the value of the flow rate of the first stream but the total flow rate should be maintained constant. In the case where the change of flow rates of the second and third streams is by increments greater than the flow rate of the first stream, the interface will become stabilized at positions which are lower than the location of the preceding stabilized lower interface. However, the rate of flow of fluid from the interval of the producing formation 12 between the location of a second stabilized upper interface and the location of the first stabilized lower interface can be readily calculated. For example, if the first stream has a flow rate of of the total flow rate of the fluid from the producing formation 12 into the borehole 10, the second stream 90% and the third stream 0%, the rate of flow from the first interval of the formation 12 between the two interfaces 34 and 42 is equal to 10% of the total flow rate as previously described. Now, if the rates of the second and third streams are varied in increments of not 10%, but say 20%, that is, so that the flow rates of the first, second and third streams are 10, 70 and 20% respectively, the two interfaces will now become stabilized at positions somewhat below the position of the lower interface at the preceding rates of flow. However, it can be readily calculated that 10% of the flow into the borehole 10 is from the increment between the upper interface at the present rates of flow and the lower interface at the preceding rates of flow.

It should be understood that the rate of flow of the first stream need not be maintained constant while the second and third streams are varied. If desired, the flow rates of each of the first, second and third streams may be varied, but the total flow rate should be maintained constant.

It should also be understood that the productivity profile log of the formation 12 may be determined by initially providing a high rate of flow in the third fluid stream and a low rate of flow in the second fluid stream while the first fluid stream is maintained at a constant rate and then repeatedly lowering the flow rates of the third streams white increasing the flow rates of the second streams so that the interfaces 34 and :2 move in an upward direction along the wall of the borehole in formation 12.

It is contemplated within the scope of this invention to provide in a producing well a method of withdrawing a fluid from a particular vertical interval of a producing formation without the fluid mixing in the well with other fluids entering into the borehole at intervals above and below the particular interval by establishing a null point at each end of the particular vertical interval. In this manner undesirable water flowing into an oil producing well can be prevented from mixing with the desirable oil.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A productivity profile logging method of discharging out of the top of a borehole fluid flowing from a vertical interval of subsurface strata into said borehole which comprises dividing fluid flowing into the borehole from subsurface strata into first, second and third streams so as to establish in the borehole a first null point of flow between the first and second streams and a second null point of flow between the second and third streams, determining the depths in the borehole of said first and second null points of flow, and adjusting the rates of flow of each of the streams while maintaining constant the sum of the flow rates of the three streams so that the first null point of flow is positioned at one of the limits of the vertical interval of subsurface strata and the second null point of flow is positioned at the other limit of said vertical interval.

2. A method of obtaining a productivity profile log of a producing formation of a well having an adjustable first tubing therein extending down to said producing formation and having a second tubing thercin extending down at least as far as the bottom of said producing formation, which comprises dividing the fluid entering into the borehole from said producing formation into first, second and third streams so as to establish in the annulus around at least one of said tubings at a location within said producing formation a first null point of flow of the formation fluid between said first and second streams, and a second null point of flow of the formation fluid between said second and third streams, determining the location of the first and second null points, measuring the rate of flow of fluid in each of the streams, and establishing first and second null points at other locations while maintaining the total fluid flow rate constant, and repeating these operations while noting the flow rates of each of the streams for each location of said first and second null points.

3. A method of making a productivity log in a borehole which comprises dividing the fluid flowing from subsurface strata into said borehole into first, second and third streams so as to establish a first null point of flow between said first and second streams and a second null point of flow between said second and third streams, determining the depths in the borehole of said first and second null points of flow, varying the rates of fluid flowing in at least two of the three streams while maintaining constant the sum of the flow rates of the three streams so as to cause said null points to move along the wall of said borehole to other depths, again determining the depths of the null points, and repeating these operations while noting the rates of flow and the nature of the fluids in each of the three streams.

4. A method as set forth in claim 3 wherein the depths in the borehole of said first and second null points are determined by determining the direction of flow of the fluid at a plurality of points in the borehole.

5. A method as set forth in claim 4 wherein the direction of the flow of the fluid in the borehole is determined by introducing a radioactive substance into at least one of the three streams between two spaced apart radiation detectors, one of said detectors being disposed above and the other below the point at which the radioactive substance is being introduced into said one stream.

References Cited in the file of this patent UNITED STATES PATENTS 2,443,680 Herzog June 22, 1948 2,540,049 Hinson Jan. 30, 1951 2,599,975 Carpenter June 10, 1952 2,869,642 McKay et a1 Jan. 20, 1959 2,991,883 Brown et al July 11, 1961 3,021,426 Wood Feb. 13, 1962 3,040,813 Tausch June 26, 1962 

1. A PRODUCTIVITY PROFILE LOGGING METHOD OF DISCHARGING OUT OF THE TOP OF A BOREHOLE FLUID FLOWING FROM A VERTICAL INTERVAL OF SUBSURFACE STRATA INTO SAID BOREHOLE WHICH COMPRISES DIVIDING FLUID FLOWING INTO THE BOREHOLE FROM SUBSURFACE STRATA INTO FIRST, SECOND AND THIRD STREAMS SO AS TO ESTABLISH IN THE BOREHOLE A FIRST NULL POINT OF FLOW BETWEEN THE FIRST AND SECOND STREAMS AND A SECOND NULL POINT OF FLOW BETWEEN THE SECOND AND THIRD STREAMS, DETERMINING THE DEPTHS IN THE BOREHOLE OF SAID FIRST AND SECOND NULL POINTS OF FLOW, AND ADJUSTING THE RATES OF FLOW OF EACH OF THE STREAMS WHILE MAINTAINING CONSTANT THE SUM OF THE FLOW RATES OF THE THREE STREAMS SO THAT THE FIRST NULL POINT OF FLOW IS POSITIONED AT ONE OF THE LIMITS OF THE VERTICAL INTERVAL OF SUBSURFACEA STRATA AND THE SECOND NULL POINT OF FLOW IS POSITIONED AT THE OTHER LIMIT OF SAID VERTICAL INTERVAL. 